1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus for imaging organs and so on within a living body by transmitting and receiving ultrasonic waves to generate ultrasonic images to be used for diagnoses. Further, the present invention relates to an ultrasonic imaging method and ultrasonic imaging program to be used in the ultrasonic diagnostic apparatus.
2. Description of a Related Art
In medical fields, various imaging technologies have been developed for observation and diagnoses within an object to be inspected. Especially, ultrasonic imaging for acquiring interior information of the object by transmitting and receiving ultrasonic waves enables image observation in real time and provides no exposure to radiation unlike other medical image technologies such as X-ray photography or RI (radio isotope) scintillation camera. Accordingly, ultrasonic imaging is utilized as an imaging technology at a high level of safety in a wide range of departments including not only the fetal diagnosis in obstetrics but also gynecology, circulatory system, digestive system, and so on.
Generally, in an ultrasonic diagnostic apparatus, an ultrasonic probe including plural ultrasonic transducers having transmission and reception functions of ultrasonic waves is used. Using such an ultrasonic probe, an object to be inspected is scanned by ultrasonic waves transmitted from the plural ultrasonic transducers, ultrasonic echoes reflected within the object are received and reception focusing processing is performed, and thereby, image information on structures (e.g., internal organs, diseased tissues, and so on) existing within the object can be obtained based on intensity of the ultrasonic echoes.
In ultrasonic imaging, it is constantly required that the balance between improvements in time resolution and improvements in spatial resolution is achieved. Especially, in the case of an ultrasonic examination of heart, high time resolution is required for observation of motion of heart wall moving at a high speed. On the other hand, in the case of an ultrasonic examination of abdomen, the structure of a tissue part is often observed in detail, and high spatial resolution is required. However, when the sound ray density is increased for higher spatial resolution, it becomes difficult to maintain the conventional frame rate.
As related technologies, Japanese Patent Application Publication JP-P2000-333951A discloses an ultrasonic imaging apparatus intended for achieving the balance between improvements in time resolution of imaging and improvements in spatial resolution of images. The ultrasonic imaging apparatus includes ultrasonic transmitting means for transmitting ultrasonic waves, reception signal forming means for forming reception signals based on echoes of the transmitted ultrasonic waves, image generating means for generating an image based on the formed reception signals, and image display means for displaying the generated image, and the ultrasonic transmitting means performs scanning of ultrasonic beam in the sound ray sequence within an imaging range by using sound rays interlaced with the sound rays at the previous scanning. According to JP-P2000-333951A, scanning the object by interlace method improves the apparent spatial resolution, but cannot improve the time resolution.
Further, Japanese Patent Application Publication JP-A-7-327986 discloses an ultrasonic image processing apparatus intended for preventing the reduction of frame rate. The ultrasonic image processing apparatus includes an ultrasonic probe segmented into plural groups according to a predetermined rule, transmitting and receiving means for transmitting and receiving waves for the respective segmented groups of the ultrasonic probe, phase-matching and adding means for phase-matching and adding echo data of all elements used for receiving waves with respect to each transmission and reception, storage means for storing data added by the phase-matching and adding means, and aperture synthesizing means for synthesizing apertures to obtain an ultrasonic image when transmission and reception of waves are performed for the number of the segments and all echo data are stored in the storage means. However, in the method of scanning the object by simultaneously transmitting plural ultrasonic beams, the influence of crosstalk cannot sufficiently be eliminated and it is difficult to sufficiently improve the spatial resolution.